The present invention relates to an overlay surface mount resistor and method for making same.
Surface mount resistors have been available for the electronics market for many years. Their construction has comprised a flat rectangular or cylindrically shaped ceramic substrate with a conductive metal plated to the ends of the ceramic to form the electrical termination points. A resistive metal is deposited on the ceramic substrate between the terminations, making electrical contact with each of the terminations to form an electrically continuous path for current flow from one termination to the other.
An improvement in surface mount resistors is shown in U.S. Pat. No. 5,604,477. In this patent a surface mount resistor is formed by joining three strips of material together in edge to edge relation. The upper and lower strips are formed from copper and the center strip is formed from an electrically resistive material. The resistive material is coated with a high temperature coating and the upper and lower strips are coated with tin or solder. The strips may be moved in a continuous path for cutting, calibrating, and separating to form a plurality of electrical resistors.
A primary object of the present invention is the provision of an improved overlay surface mount resistor and method for making same.
A further object of the present invention is the provision of an improved overlay surface mount resistor and method for making same which reduces the number of steps and improves the speed of production from that shown in U.S. Pat. No. 5,604,477.
A further object of the present invention is the provision of an improved overlay surface mount resistor and method for making same wherein the resulting resistor is efficient in operation and improved in quality.
A further object of the present invention is the provision of an overlay surface mount resistor and method for making same which is economical to manufacture, durable in use and efficient in operation.
The foregoing objects may be achieved by a surface mount resistor comprising an elongated resistance piece of electrically resistive material having first and second end edges, opposite side edges, a front face and a rear face. The resistance piece of resistive material includes a plurality of slots formed in its side edges that create a serpentine current path for current moving between the first and second ends of the resistor.
First and second conductive pieces of conductive metal are each formed with a front face, a rear face, first and second opposite side edges, and first and second opposite end edges. The first and second conductive pieces each have their front faces in facing engagement and attached to the front face of the resistive material and are spaced apart from one another to create an exposed area of the front face of the resistive material therebetween. A dielectric material covers the exposed area of the front face of the resistive material.
The method of the present invention includes taking elongated resistive strip of electrically resistive material having first and second opposite ends, an upper edge, a lower edge, a front flat face, and a rear flat face. The method includes joining a first elongated conductive strip and a second elongated conductive strip of conductive material to the front flat face of the resistive strip in spaced relation to one another so as to create an exposed portion of the front flat face of the resistive strip between the first and second conductive strips. The joined strips are then sectioned into a plurality of separate body members. Next a plurality of slots are cut through the exposed portion of the resistive strip to create a serpentine current path in the resistive material of each of the body members. Next the resistive strips of each body member are encapsulated in a coating of electrically insulating material.
According to one feature of the invention, the attaching step comprises attaching an elongated wide conductive strip over substantially the entire surface of the front face of the resistive strip and then removing a central portion of the wide conductive strip to create the first and second elongated conductive strips and the exposed portion of the elongated resistive strip therebetween.